Shadowmere

Shadowmere is the name of your mighty steed that stays with you once you've completed The Cure For Madness as part of the Dark Brotherhood questline. He doesn't cost you a single septim, plus he has more Stamina and Health than any standard horse, making him harder to kill by enemies! These attributes make him a combat-ready stallion, who can add yet another body to the Insane Crown Posse. If you lose Shadowmere for whatever reason besides him dying, he will spawn back outside of the Darkstar Sanctuary provided the main Dark Brotherhood quests are completed otherwise he will spawn outside of the Dark Brotherhood sanctuary